Manufacture of trimethyl phosphate



United States Patent ()fiice g 3 053 879 MANUFACTURE oFTRiMETHYL PHOSPHATE Gerald W. Kottong, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delainert gas, such as ethylene, to the reaction zone to provide countercurrent or crossflow stripping of the hydrogen chloride, the quantity of the gas added being from about 4 to 8 moles per mole of hydrogen chloride produced as 5 a by-product, the by-product hydrogenchloride and gas ware being removed from the top of the zone and the product T No Drawmgk g if g i i 834962 trimethyl phosphate being recovered at the bottom of the reaction zone. An external heat exchanger can be'em- This invention relates to the production of trimethyl ployed to remove the he at of reaction or alternately a phosphate and especially to an improved process for large 10 sufiicient quantity of liquid alkyl chloride (methyl chloscale commercial manufacture thereof. ride or ethyl chloride) can be added to the reaction mix- Many alkyl and aryl phosphate esters are presently cure to remove by vaporization the heat of reaction and produced on commercial scale and are extensively used the heat of solution of the hydrogen chloride in the both as additives to gasoline and as plasticizers for therreaction mixture. When internal cooling is employed, moplastics. The simplest of the organo phosphate esters, from 3 to 4 moles of alkyl chloride are used permoleof trimethyl phosphate, is not manufactured at the present hydrogen chloride produced (9 to 12 moles pen-mole of time even though it is a highly effective gasoline additive phosphorus OXYFhl OIIdE). To reduce the cool ng load (US. 2,427,173) and even though it would be mu h in the reactor, it is frequently desirable to pro-saturate cheaper than the phosphate esters presently in use. Its the methanol WIT-h hy g ehloflde before feedlhg 0 economy is based upon its high phosphorus content (22 h a If d refillX eohqehsel' can be p percent of trimethyl phosphate) whereas with tricresyl at the p o the reactor to cohhhhohsly h phosphate, .for example, the phosphorus content is only hqhld y chloride to the l'eaetol: 0 9 h qn about 12 percent. The major deterrent in the use of The Phosphorus Y 1d /m thanol'mole ratio trimethyl phosphate has been the lack of an adequate P e y between about The Tesldence process to economically produce the same. By all known 25 tlme 111 {he Teaetloh Zone Should h b g t h n processes the yields of trimethyl phosphate have been of ahout one 110111 and P e y the resldehce mm 15 mm: the order of 20-40 percent. Among the many reasons tamed between 10 mlhlltes and l The h for poor yields includes the formation of by-product Perature 0f h feactloh can range Q about 0 to methyl chloride and acids, even at temperatures as low o although 11; 18 Preferred t0 malhtalh the y r q e as 7Q 30 from 10 to 30 C. The pressure of the reaction is 1113.111: It is accordingly an object of this invention to provide tamed from ahlwsphefle about P- -g- Hlghelf an improved process for the manufacture of trimethyl Pressure h he used deslred- 1 phosphate. Still another object is to provide a process The Teactloh Z011e 1S best s parated mto stages, s y which is suitable for use on commercial scale to give frohl 3 stages, In Order to Permlt h Y the high yields, i.e., above about 85 percent of trimethyl deslred "methyl P Ph wlthout the formatlon phosphate, and which at the same time avoids the for- Othef phosllfhofus-eohtalmhg YP e results e mation of undesired by-products. Another object is to obtained Wlth from- 4 to 10 stages- In 9 mstancesi'il-t provide a process in which the product can be simply and de1mb1e to Fmploy PackedfeaFwr usmg easily recovered by distillation without the need for neu- 40 gl gi i fi i Stuch as i g m 1 tralization of the by-product hydrogen chloride. Still y P 9 ac remove 99 e o om anothfir obbct to mvide a rocess which can be vertical reaction zone can be d stilled to recover the trip p methyl phosphate in high purity, usually from 95 to tegrated with a methyl chloride or ethyl chloride process, 100 percent I thereby i the l anfihefliclent lutlhzanon The following are typical examples which illustrate the by'product y rogen c onde Wlt out cost y Separa' process of this invention. The examples of Table I were StePsi carried out in a vertical column having 5 plates. The has now been found that exceptlonal we of methanol and phosphorus oxychloride were fed on the top methyl phosphate can be obtained if a reaction zone is plate d h h l on the bottom Plate The reaction established in which methanol and phosphorus oxychlomixture was maintainedat about 20 C. All quantities ride are continuously fed to the zone under reaction conare given in moles. 1

Examples I 11 111 IV v VI v11 fvr'n Feed (moles): P0013. 0.3928 0. 3273 0.3382 0.3600 0. 3600 0.3928 0. 5074 1-0 MeOH 1.8750 1.0750 1.7250 1.9250 1.4500 1.0000 2.9250 4. 92 02H," 0.8100 4.8040 5.1790 4.6841 4.0120 5. 7395 5. 0371 12.07 Conversion, percent. 94.9 97.2 97.9 97. 94.4 94.8 91.4 97.7 TMP yield percer t 80.4 85.4 85.3 85.8 83.1 79.5 74.1 88.3 Res1dencet1n1e,m1nutes 39.3 42.7 46.3 48.4 44.7 36.9 24.2 1928 Percent H01 removed- 68.1 00.3 02.5 02.4 75.2 74.4 53.0 72.9 Cleavage, percent 8.4 14.6 14.7 14.2 14.7 20.5 10.4 11.7 Temperature, C 20 20 20 20 .20 20 20 20 M001 (liquid) 9. 11 Prod. dist., weight percent:

Hol 17.75 17.85 15.59 13.78 13. 72 18.70 14:0 21.95 19.49 24.74 9.92 12.79 23.40 3:6 8.28 8.00 7.90 10.50 14.27 5.61 8.0

NorE.-Me=Methyl.

ditions, the methanol being fed in at least 30 percent excess based on stoichiometry, simultaneously feeding an The above product was thereafter distilled in two successive columns to obtain pure trimethyl phosphate.

The first column was operated with an overhead temperature of about 38 F. and a bottoms temperature of 235 F. The overhead was primarily methanol and HCl. The bottoms were passed to a second column wherein the trimethyl phosphate was distilled at an overhead temperature of 190 F. and a bottoms temperature of 390 F.

Example IX The process of this example has been carried out in separate staged stirred pot reactors, excellent results being obtained with three pots in series. The phosphorus oxychloride (1.5 moles per hour) was fed to the first reactor along with 7.5 moles per hour of methanol. The reaction mixture was removed near the bottom of the first reactor and fed to the second reactor near its top. Likewise, the reaction mixture from the second reactor is removed from the bottom thereof and fed to the third reactor near the top thereof. Each of the mac tors was maintained by cooling coils at a temperature of 20 C. The residence time in the first reactor was 10 minutes, the second and third reactors 30 minutes. To each of the reactors was fed 12 moles per hour of nitrogen gas in order to provide crossfiow stripping of the hydrogen chloride formed in the reaction. The mixed hydrogen chloride-nitrogen gas stream was removed from the top of each of the stirred reactors. The trimethyl phosphate reaction mixture was passed from the third reactor to a distillation column operated at an overhead temperature of C. and bottoms temperature of 110 C., the pressure in the column being about 20 mm. of mercury. The purified trimethyl phosphate was thereafter removed from the bottom of the first column and fractionated in a second column operating at overhead temperature at the boiling point of the trimethyl phosphate; the column also is operated at a reduced pressure, i.e., about 20 mm. of mercury. The acids formed in the reaction were removed as bottoms of the second column. The overhead from the first column was primarily methanol containing dissolved HCl. This overhead gas mixture waspartially condensed and returned to the first reactor. The uncondensed HCl and traced quantities of methanol can be recovered or used in other processes. The average yield of distilled purified trimethyl phosphate after many hours of operation was 75 percent based upon phosphorus oxychloride charged to the first reactor.

When the above reaction is repeated using countercurrent stripping, i.e., passing the nitrogen gas from the third reactor through the second reactor and then through the first reactor, similar results are obtained. Also, when the nitrogen is replaced with other inert gases, such as natural gas containing predominantly methane or when using ethane or ethylene, similar rewhen present, alkyl chloride can be passed directly to the ethyl chloride plant without pre-separation of the alkyl chloride from the by-product hydrogen chloride.

The overhead containing hydrogen chloride and ethylone are passed to a reactor containing aluminum chloride or other Friedel-Crafts catalyst dissolved in ethyl chloride solvent and the hydrogen chloride reacted therein with ethylene (U.S. 2,838,578). This reaction is suitably carried out at elevated temperatures and pressures, that is above about 30 C. and at a pressure over 2 atmospheres. It has been found that the highly desirable range of operating temperatures is between 30 C. and 200 C. and still more preferably between 40 and C. Similarly, under these temperature conditions operating pressures between 2 to 30 atmospheres and preferably between 6 and 14 atmospheres are beneficial in carrying out this process.

I claim:

1. Process for the manufacture of trimethyl phosphate comprising establishing a reaction zone containing from about 3 to 20 stages, continuously feeding methanol, phosphorus oxychloride and an inert gas to said zone, said methanol being fed in at least 30 percent excess based on stoichiometry, said inert gas being employed in .a quantity of from 4 to 8 moles per mole of hydrogen chloride formed in said reaction and, while maintaining the temperature of the reaction zone within a range of from about 10 C. to about 30 C.

2. The process of claim 1 wherein the reaction zone has from about 4 to about 10 stages.

3. The process of claim 1 wherein the phosphorus oxychloride:methanol ratio is from about 1:3.9 to about 1:8.

4. The process of claim 1 wherein the residence time within the reaction zone is from about 10 minutes to about 30 minutes.

5. A process for the manufacture of trimethyl phosphate comprising establishing a staged reaction zone having from about 4 to about 10 stages, maintaining a temperature of from about 10 C. to about 30 C. therein while continuously feeding methanol, phosphorus oxychloride and an inert gas to said zone, the methanol being fed into the reaction zone in an excess of at least 30 percent based on the stoichiometry, the phosphorus oxychloride being fed into the reaction zone at a phosphorus oxychloridezmethanol ratio of from about 1:3.9 to about 1:8, the inert gas is employed in a quantity of from about 4 to about 8 moles per mole of hydrogen chloride formed in the reaction and is a gas selected from the group con sisting of ethylene, methane, ethane and natural gas, while providing a residence time within the reaction zone of from about 10 to about 30 minutes.

6. Process for the manufacture of trimethyl phosphate comprising establishing a series of three staged reaction zones, continuously feeding phosphorus oxychloride and methanol to the first zone, said methanol being fed in at least 30 percent excess based on stoichiometry, while removing the reaction mixture from the first zone and feeding same to the second zone, and removing the reaction mixture from the second zone and feeding same into the third zone, the reaction zones being maintained at a temperature of about 20 C. while providing a residence time in the first zone of about 10 minutes and a residence time in the second and third zones of about 30 minutes, while feeding natural gas into each of the said zones to effect maximum removal of hydrogen chloride byproduct.

OTHER REFERENCES Gerrard: J. Chem. Soc. 1940, 1464-1469. Orloft" et al.: I. Am. Chem. Soc. 80, 734-739 1958). 

1. PROCESS FOR THE MANUFACTURE OF TRIMETHYL PHOSPHITE COMPRISING ESTABLISHING A REACTION ZONE CONTAINING FROM ABOUT 3 TO 20 STAGES, CONTINUOUSLY FEEDING METHANOL, PHOSPHORUS OXYCHLORIDE AND AN INERT GAS TO SAID ZONE, SAID METHANOL BEING FED IN AT LEAST 30 PERCENT EXCESS BASED ON STOICHIOMETRY, SAID INERT GAS BEING EMPLOYED IN A QUANTITY OF FROM 4 TO 8 MOLES PER MOLE OF HYDROGEN CHLORIDE FORMED IN SAID REACTION AND, WHILE MAINTAINING THE TEMPERATURE OF THE REACTION ZONE WITHIN A RANGE OF FROM ABOUT 10* C, TO ABOUT 30* C. 